1. Field of the Invention
The present invention relates to a thin film magnetic head having a heater that generates heat to expand a reproducing element and a recording element toward a recording medium.
2. Description of the Related Art
A thin film magnetic head used for, for example, a magnetic disk apparatus includes a reproducing element that reads out magnetic recording information from a recording medium using magnetoresistance and a recording element that applies a recoding magnetic field to the recording medium to record various information items on the recording medium. The reproducing element has a multi-layer film that exhibits magnetoresistance between a lower shield layer and an upper shield layer opposite to each other at a predetermined gap therebetween on a surface facing a recording medium. The recording element is formed on the upper shield layer, and includes a pair of magnetic layers opposite to each other with a magnetic gap layer interposed therebetween on the surface facing a recording medium, and a recording coil that applies a recoding magnetic field to the pair of magnetic layers. In recent years, a thin film magnetic head has been proposed which includes a heater that is supplied with power and generates heat that is provided in the vicinities of a reproducing element and a recording element. In the thin film magnetic head including the heater, heat generated by the heater causes the reproducing element and the recording element to protrude toward a recording medium. Then, the gap (the lift of the head) between the recording medium and an element portion is locally narrowed, which makes it possible to improve recording and reproducing characteristics.
However, the amount of protrusion of the element portion due to thermal expansion depends on the external environmental temperature as well as the amount of heat generated by the heater. For example, as the external environmental temperature increases, the amount of protrusion of the element portion becomes larger. Therefore, when the external environmental temperature is high during the operation of the heater, there is a fear that the element portion will come into contact with a recording medium and the element portion and the recording medium will be damaged. In order to solve this problem, a method of reducing the amount of heat generated from the heater to reduce thermal expansion of the element portion has been proposed. However, the method of reducing only the amount of heat generated from the heater is insufficient to solve the above-mentioned problem since the thermal expansion of the element portion is also generated due to the external environmental temperature. That is, the thermal expansion of the element portion is generated due to both the heat generated by the heater and the external environmental temperature (when the external environmental temperature is high) or only the heat generated by the heater (when the external environmental temperature is low). The amount of protrusion of the element portion varies according to the external environmental temperature. When the amount of protrusion of the element portion varies, the gap between the element portion and the recording medium varies, which results in low reliability.